Clean the rhubarb and cut into small slices. Put all the ingredients, except the cornstarch, in a pot and bring to a boil.
When the rhubarb boils, reduce the temperature and simmer until it is quite soft. Stir frequently.
Stir some cornstarch with water and thicken the compote.
Remove the compote from the heat and let it cool.
Heat the milk lukewarm in a small saucepan, add the yeast and stir until it has dissolved.
Put flour, butter, sugar, salt and the egg in a mixing bowl. Add the yeast milk and mix with the dough hooks at slow speed. Then knead at the highest speed into a dough until it releases from the bowl (about 8 minutes).
Cover the bowl with a towel and leave the dough in a warm place for about 30 minutes.
Knead all ingredients in a small bowl to crumble.
Briefly knead the dough and roll out on the floured work surface to a rectangle of approx. 30 x 60 cm.
Spread the compote on the dough and cut the dough into three strips. Roll them up starting from the long side. Plait the three rolls.
Place the dough on a baking tray covered with baking paper, cover with a towle and let it rest for about 15 minutes.
Brush the loaf with the yolk-milk-mixture, spread the crumbles on it and bake in a preheated oven at 175°C for approx. 30-35 minutes. Remove and allow to cool.